SRS-A (Slow Reacting Substance of Anaphylaxis) was first described in 1940 and shown to be released from monkey lung in 1966. Although SRS-A is well known as a mediator of bronchial asthma, the biochemical mechanism of its synthesis remains unknown. The precursors of SRS-A and the enzymms involved in its formation have not yet been described. The purpose of this study is to examine a number of compounds for their ability to increase the biosyntheis of SRS-A and for their possible incorporation into this biologically active compound.